In the related art, power circuits including switching regulators or linear regulators are used to supply appropriate power-supply voltages to a number of devices included in electronic apparatuses. When linear regulators receive variations in power-supply input to amplifiers (hereinafter referred to as noise), the linear regulators have capabilities to reduce the noise. Power supply ripple rejection ratio (PSRR) characteristics are known as an index indicating a capability to remove noise in a linear regulator. The PSRR characteristics are expressed as a ratio of a variation in input voltage to a variation in an output voltage from the regulator. The variation of the output voltage to a variation (noise) of the power-supply voltage or the reference voltage becomes smaller, and the resistance to noise is improved, as the PSRR becomes higher. To improve the PSRR characteristics, methods of stabilizing a reference voltage source of a linear regulator, adjusting frequency characteristics of an open-loop, or increasing a gain have been considered. In these methods, however, a problem occurs in that a circuit area of the linear regulator increases or the current consumption increases.